The present invention relates to an oil-pressure device. More specifically, the present invention relates to an oil-pressure device which operates with an oil-pressure cylinder unit to actuate a working device which performs prescribed operations on objects such working device being, for example, a crusher used for dismantling concrete buildings.
Referring to FIGS. 7 and 8, a crusher as shown in the drawings is generally used at sites where a concrete building is to be demolished in order to crush or cut concrete pieces, steelwork, and the like. This crusher comprises a movable upper jaw 2, driven by an oil-pressure operated cylinder unit 1, the cylinder unit 1 having a cylinder C in which is carried rod R to one end of which is attached piston 17 slidable in the cylinder, extension/retraction movement of the rod in the cylinder being effected with oil pressure acting on opposite faces of piston 17.
The cylinder unit 1 is attached at an end via a pivot shaft 5 to a fixed lower jaw 3. At an opposite cylinder end, the cylinder rod R is attached by pivot shaft 6 to upper movable jaw 2. The fixed lower jaw 3 is attached to an end of a power shovel boom or similar unit. Extension/retraction of the cylinder rod R in cylinder C, effects pivoting of upper jaw 2, which is pivoted to the lower jaw with pivot 4, between closed and open positions of same in respect to the fixed jaw 3.
When the crusher is used to crush a piece of concrete or the like, the retraction of cylinder rod R causes movable upper jaw 2 to open wide. A piece of concrete is then scooped onto fixed lower jaw 3. Then, the extension of cylinder rod R causes movable upper jaw 2 to close against the concrete piece, and the oil-pressure force effects a further closing movement of jaw 2 against the concrete piece and crushing it.
In the prior art crusher described above, when fixed lower jaw 3 and movable upper jaw 2 are used to crush pieces of concrete and the like, the opening of movable upper jaw 2 is achieved by retracting cylinder rod R. Therefore, the amount of oil needed for retraction is decreased by the volume of the rod, and the opening operation for movable upper jaw 2 is relatively fast. In contrast, once movable upper jaw 2 has been opened, cylinder rod R is extended during an interval in which no load is applied, from the beginning of the closing operation of movable upper jaw 2 to its contact with the piece of concrete. A large amount of oil is needed to extend cylinder rod R, and although the closing force of movable upper jaw 2 is strong, the speed at which this occurs is very slow. Thus, it has been extremely difficult to speed up operations.